title: Study on the role of tyrosine side-chains at the active centre of emulsin beta-D-glucosidase.
abstract: The role of exposed tyrosine side-chains in enzyme-catalyzed reaction by sweet almond emulsin beta-D-glucosidase (beta-D-glucoside glucohydrolase, EC 3.2.1.21) has been studied using N-acetylimidazole as the specific reagent. The changes in activity, binding affinity and kinetic parameters (Km, V) as a result of acetylation of the phenolic hydroxyl groups have been determined. The acetylation increased the Km values of both beta-glucosidase and beta-galactosidase activities, whereas V remained unchanged. Similarly, the binding affinity for immobilized phenyl beta-D-glucopyranoside decreased appreciably. After the removal of the acetyl groups the enzyme regained 96% of the original activity. It is concluded that the tyrosine moieties, located in the active centre of the enzyme, have both glucoside and galactoside binding functions.
mesh_terms: D000107:Acetylation; D005959:Glucosidases / Q000378:metabolism*; D007093:Imidazoles / Q000494:pharmacology; D007700:Kinetics; D012639:Seeds / Q000201:enzymology*; D013439:Sulfhydryl Reagents / Q000494:pharmacology; D014443:Tyrosine; D001617:beta-Glucosidase / Q000378:metabolism*
chemical_list: D007093:Imidazoles; D013439:Sulfhydryl Reagents; D014443:Tyrosine; D005959:Glucosidases; D001617:beta-Glucosidase; C012160:N-acetylimidazole